Molten salt systems are currently being used to treat used metal fuel from nuclear reactors. Indeed, an electrometallurgical treatment process has been developed by Argonne National Laboratory and is currently deployed at Idaho National Laboratory for the treatment of 25 MTHM (Metric Tons of Heavy Metal) of metal uranium and uranium alloy fuels from Experimental Breeder Reactor-II (EBR-II) and the Fast Flux Test Facility. In this process used, or spent, metal uranium alloy fuels are broken up, or chopped, and immersed in a molten salt electrolyte of LiCl—KCl—UCl3 at 500° C. An electric potential is applied to anodically dissolve uranium metal from the used fuel and simultaneously deposit refined uranium metal on a solid cathode, from which the uranium metal fuel is recovered for reuse. In this electrorefining process, transuranic products, including Pu, Np, Am and Cm, and reactive fission product metals, including Cs, Rb, Ba, Sr, Y, Nd, Ce, La, Pr, Sm, Eu, and Gd, partition from the used fuel to the molten salt via exchange uranium trichloride per the following general reaction mechanism:M+UCl3→MClx+U  (1)
where M=transuranic or reactive fission product metals.
Non-reactive, or noble metal, fission products, including Zr, Mo, Ru, Pd, Tc and Rh, remain with the undissolved cladding hulls at the anode, where they are subsequently removed and processed into a metallic waste form for disposal. Reactive non-metal fission products, including Te, Se, I and Br, diffuse into the electrorefining salt as anions. After sufficient accumulation in the electrorefining salt, transuranic constituents may be co-recovered with uranium using a liquid cadmium cathode to produce a group uranium/transuranic metal product. The remaining reactive fission products in the electrorefining salt (with or without the transuranic constituents) may be processed into an engineered ceramic waste form for disposal. The prescribed electrometallurgical treatment process is well suited for a metal fuel cycle, and variations of this process are practiced in fuel recovery.
In an effort to extend the electrometallurgical treatment process to oxide fuels, a process has been developed by researchers at Argonne National Laboratory to convert uranium oxide to metal as a front-end step to electrorefining. In this process, commonly referred to as oxide reduction or electrolytic reduction, declad and crushed uranium oxide fuel is loaded into a permeable steel cathode basket and immersed in a molten salt electrolyte of LiCl-Li2O at 650° C. An electric potential is applied between the oxide fuel loaded cathode basket and an immersed platinum anode to electrochemically reduce the uranium, oxide to metal, thereby liberating its oxygen ions to the molten salt where they are simultaneously oxidized to oxygen gas at the anode. The reduced uranium oxide fuel is then amenable to the prescribed electrorefining process. Indeed, electrolytic reduction and electrorefining has been applied to used uranium oxide fuel, where refined uranium metal, devoid of fission products, has been successfully produced at bench, or small, scale. Applications of the oxide reduction process are currently being pursued, although this technique has not yet been deployed on a large scale for use with used uranium oxide fuels.
In light of the above-discussed, there is a need for a method to process uranium oxide fuels using a single molten salt system without converting uranium oxide to metal.